Various fluid control valve technologies are well known in the prior art, in looking particularly at relatively large size heavy duty control valve apparatus that are generally incorporated at the outlets of large hydraulic conduits, particularly in river, dam, and canal outlet works, or bypass lines, and energy dissipators that are either submerged (completely within the fluid) or free releases (open to atmosphere) at the valve outlet. The purpose of these valves is to variably restrict fluid discharge flow through the outlets, and are preferably controllable between a fully open position and a fully closed position, wherein in the fully closed position the valve has a minimal amount of fluid leakage that is acceptable for its intended use. Prior art heavy duty control valve and/or gate apparatus has included jet flow gates, fixed cone valves, tube valves, slide valves, wheel valves, mounted valves, radial valves, top seal radial valves, roller gate valves, needle valves, hollow jet valves, ensign valves (upstream control), and butterfly valves. These valves are positioned in line with the outlet and by their design nature interfere or are “in stream” with the fluid flow as a means for controlling the fluid flow through the valve outlet. Therefore, the aforementioned valves are generally of the type that are mounted within or inside of the conduit and extend with a control structure or apparatus from the inside of the conduit to the exterior of the conduit.
There are inherent disadvantages to mounting the valve within the conduit and in the fluid flow stream; firstly, the valve surface may contain changes in curvature, discontinuities, vanes, or shafts, and the like which make it difficult for the flow to follow the surface and may cause flow separation that can lead to cavitation. This aforementioned cavitation in the conduit stems from low hydraulic pressure pockets, that reach the fluid's vapor pressure immediately downstream of the valve surface (for example a surface discontinuity) at the fluid conduit interface, wherein the pocket becomes a gas trapped within the liquid. Picturing a valve inside of a conduit disrupting fluid flow one could draw the analogy to an airplane wing passing through a fluid such as air and by necessity the wing passing through the air creates high and low pressure pockets. In the fluid in a valve this causes difficulty in that the low pressure pockets typically cause a phase change of the fluid from a liquid to a gas, wherein the gas bubbles recompress in the fluid downstream of the valve back to their original phase of being a liquid. The problem with this recompression of the gas bubble within the fluid flow is that it occurs quite violently and can cause damage to valve surfaces in addition to causing a high level of noise. If the recompression of the gas bubble occurs not adjacent to a valve surface, say in midstream flow in a conduit, the result is typically only noise and not valve surface damage, however, the recompression of the gas bubble can hinder the passage of debris within the fluid through the valve. The second inherent disadvantage to mounting the valve within the conduit and in the fluid flow stream is that when the valve is in the fully open position, the valve still remains to some extent in the conduit or in the fluid flow stream. This results in the inability of a valve to allow full free flow of the fluid within the hydraulic conduit, in addition to causing some disruption of fluid flow, which again can increase the risk of fluid cavitation as previously described. In addition, maintenance and inspection of the aforementioned valves is made more difficult by having the valve operational structure within the hydraulic conduit, making access to the valve operational structure more time consuming.
The aforementioned problems with the previously described prior art valves have led to the development in the prior art of another type of valve that uses only the external area of the conduit for the valve structure or apparatus. One type of this prior art valve is called a clamshell gate type of hydraulic flow control valve. The principal advantage of the clamshell type valve is that the interior of the hydraulic conduit is completely unobstructed when the clamshell type valve is in a fully open position and thus helps reduce the incidence of fluid cavitation as previously described. However, it must be noted that a clam shell type valve is typically a hydraulic conduit termination type valve, in other words the clam shell type valve is typically discharging submerged at the end or termination of the hydraulic conduit within the fluid or discharging at the end or termination of the hydraulic conduit to the open atmosphere. It would not be possible for the clamshell type valve to engage in fluid flow control within a hydraulic conduit fluid flow system wherein the clamshell type valve outlet would continue fluid within a hydraulic conduit.
However, clamshell type valves by their very nature in the design have a number of their own inherent problems; firstly, when the clamshell gate members are in the partially or fully open position, the conduit outlet is entirely upstream of the gate leading edge lips, which in turn causes the fluid flow discharge to “fan out” from the conduit outlet, thus creating an unclean jet and associated problems when the fluid flow discharge is into a confined region such as an open flow channel, canyon, and the like by increasing the potential for fluid flow erosion damage extending perpendicular from the direction of the fluid flow out of the conduit outlet. Secondly, another disadvantage of clamshell type valves in is the complexity of the mechanical structure required to pivotally open the clamshell valve members, which must be substantially symmetrically moved to one another to create a substantially balanced hydraulic load against the gate members. One prior art solution in this area is to use a single clamshell radial member to close over the conduit outlet which eliminates the mechanical complexity for a symmetrically opening pair of clamshell gate members, however, the hydraulic loads are significantly unbalanced as against the clamshell gate and require a heavy duty gate attachment and pivot/control structure. A third identified problem with clamshell type valves concerns fluid sealing between the conduit outlet and the clamshell gate members when the valve is the fully closed position. The significance of this third problem depends upon the application and use of the clamshell type valve that dictates an amount of acceptable leakage of the fluid when the valve is in the fully closed position. Resulting in that if leakage of the fluid is not tolerable to requiring a very small leakage of the fluid when a clamshell type valve is in a fully closed position, the requirement for the sealing becomes more complicated between the conduit outlet and the clamshell gate members.
A few similar examples in the prior art are in the U.S. Pat. No. 3,998,426 to Isbester that discloses an apparatus for controlling fluid discharge through an outlet of a conduit utilizing clamshell type gates that are pivotal or operable through either a plate slot arrangement or a yoke link arrangement. In Isbester the seal between the conduit outlet and the gates is either an axially movable collar with a seal on its end or an annular seal on the conduit end itself without the axially movable collar. In addition, Isbester discloses the use of a lip seal between the gate halves interface when the gates are in the fully closed position. Isbester mostly concerns the detail of the gate movement and control structure and does not go into any substantial detail relating to seal design or seal material specifics in association with a required valve closed condition leak rate that would be required for specific applications. In U.S. Pat. No. 2,742,324 to Kerensky disclosed is a hydraulic discharge regulator utilizing a single pivoted clamshell gate for the end of a conduit. Kerensky also discloses a metal sealing ring or alternatively an inflatable sealing ring between the end of the conduit and the clamshell, however, no additional detail on the sealing is disclosed. Similar to Kerensky in U.S. Pat. No. 3,123,334 to Hitz disclosed is a rotary gate valve also utilizing a single pivoted clamshell gate having a flow opening and a solid portion to close the end of a conduit with the seal between the conduit end and the gate being an conventional o ring that is in a prepared groove located at the end of the conduit, however, beyond the use of a conventional o ring, Hitz discloses no additional detail as to the specifics of the sealing between the end of the conduit and the gate. In this same area in using a single clamshell gate in U.S. Pat. No. 5,692,470 to Sattler et al. discloses a throttle body that acts as a valve utilizing a single pivotally attached clamshell gate that has an annular seal between the gate and the throttle body with an option to spring bias the gate against the seal. However, Sattler et al. is differentiated in that the valve is a housing body as opposed to a conduit end, thus allowing more surface area for sealing, gate stops, and mounting of the gate as against the body.
One final prior art example that utilizes flat sliding plates as against a conduit outlet being opposed to the aforementioned pivoted clamshell gates is in U.S. publication number US2002/0125455 A1 to Kubitschek et al. that discloses a modified Isbester flow control gate valve having two approximately 45 degree inclined flat surfaces that have an opening the same size as the conduit internal diameter. In Kubitschek et al. the water flow is controlled by a rectangular pair of flat gate leaves that are operable to slide upon the inclined flat surfaces being held in place by gate guides with the sliding facilitated by an anti friction material. Also, in Kubitschek et al. the movement of the gates is controlled by hydraulic actuators and sealing between the gates on the inclined flat surfaces uses a conventional o ring, also disclosed is a lip seal visor being an external separable assembly having its own positional actuator, there is no disclosure related to the seal required between the o ring and gate interface when the valve is in the fully closed position.
What is needed is a clam shell type valve that retains the inherent advantages of a clam shell type valve as previously discussed being principally the unobstructed fully open position flow of the fluid within the hydraulic conduit in conjunction with the reduced incidence of fluid cavitation, and at the same time overcoming the inherent disadvantages of the clam shell type valve for the fluid to fan out at the conduit outlet, a simpler structure for substantially symmetrically controlling the clamshell gates movement, and the gates position to one another, and finally to have a more sophisticated sealing system to reduce the fluid leakage rate when the clam shell type valve is in the fully closed position.